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What is the maximum lateral deviation allowed on an RNAV route?
If an airliner (enroute via IFR rules) discovers a thunderstorm ahead, how much lateral deviation is allowed before a clearance from ATC needs to be obtained ?
Is the width of an RNAV corridor only for navigation errors or also for intended deviations ?

I assume this question springs from the Delta incident over China. RNAV routes have various widths, China has 20 km if I was informed correctly. That doesn't allow a pilot to fly 10km of the centreline, there is uncertainty in the navigation to be taken into account as well.

Are you asking about a specific country or set of regulations, e.g. FAA, EASA, other?

4 nm from centerline or 8nm total width of airway.
You are not required to instantly turn when transitioning between airways.  Required navigational precision for most enroute segments is 2 nm.  Being conservative and always assuming an operational error of 2nd means any observed deviation of more than 2 nm is a red flag.
Intentionally deviating within the course width is not prescribed within the regulations, but then there's no regulation prohibiting or allowing fly by (fly over is sometimes mandated).

If the aircraft is under ATC control then no deviation is allowed except in an emergency. A pilot who wants a course change would need to request it from ATC and obtain a clearance. If the flight is not under ATC control and wants to divert then it's pilot's discretion, he/she would notify ATC of the change if receiving some sort of service.

IFR automatically means ATC control, does it not?

More or less. The aircraft could be flying VFR-on-top in which case altitude changes within the predefined range do not require ATC approval (the plane already has it) but do require VFR-style look-and-avoid.

@FreeMan Not in the middle of the Pacific!


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If the EPU (Emergency Power Unit) on a modern fighter jet fails, will the aircraft drop out of the sky?
If the EPU (Emergency Power Unit) and batteries plus engines fail on a modern fighter aircraft, basically they will fall out of the sky, there is no dead stick landing - is this correct?

There may also be a RAT on board

I don't think anyone really expects fighter to do a dead-stick landing under any conditions. In many mission profiles the aircraft is too low to glide anywhere useful anyway.

Are you asking if there are other power sources that could help with a dead-stick landing, or whether an aircraft is controllable without any electrical/hydraulic power?

@JanHudec tell that to the high altitude interceptor pilots... Not everyone is down in the dirt playing the penetration bomber game.

@jwenting: They are ever since high-altitude SAMs rendered flying above the enemy's air defences obsolete as a strategy for avoiding getting shot down, way back in the sixties.

@Sean tell that to the mid level and high level  bomber pilots over Afghanistan and Syria.

How Are Modern Fighter Aircraft Controlled?
The F16 was the first US military aircraft to be designed around the revolutionary fly-by-wire concept.  This meant there were no direct mechanical linkages between the cockpit and major control surfaces, and that all pilot input was electronically carried to the hydraulic system via wire.  However, since the F16 burst into the scene, there have been further major advancements in aircraft systems design.  Late Gen 4 aircraft, such as the F/A 18 Super Hornet, are designed around a concept now called control-by-wire.  Control-by-wire aircraft not only have removed mechanical linkages to the hydraulic system, but now the pilot is only a voting member.  This means that all input is received by a computer bank that then computes what it thinks the pilot is intending to do, and then autonomously operates the control surfaces to achieve the effect.  This means that Gen 4 aircraft rely heavily on both computer integrity (and there are plenty of self-healing backups), and the power required to run those systems.
Power Failure
If there was a catastrophic total electrical failure and the only remaining power supply was the battery, the only option is for the pilot to restart a generator.  In the event that the engines were operating and all power generation was destroyed, the aircraft would only be flyable for the duration which the battery could provide power to the aircraft--that's a very limited duration.
Possible other scenarios could include a dual-engine failure. In this instance, the aircraft may be able to fly fast enough to generate enough airflow down the turbine to turn the generator and perform an airstart, but this would only be useful in a dual engine failure, and only if there was enough altitude and airspeed to trade to make it a realistic option.  Otherwise, the battery would probably be used to power the APU, and attempt a relight.  Again, if both engines relit and the generators (including the APU) failed to produce power, then the aircraft would not be flyable.
But what about the RAT?
Although currently in limited use on some trainer aircraft like the T-45, modern fighter aircraft do not use a RAT.
So what usually happens in a total electrical failure?
If the aircrew cannot get a generator back online then they eject.

Wikipedia (in a nearly-unreferenced article) says that RATs can generate electrical power i.e. "RAT will power vital systems (flight controls, linked hydraulics and also flight-critical instrumentation)", and that, "RATs are common in military aircraft which must be capable of surviving sudden and complete loss of power".

Wikipedia is often wrong, and this is one of those instances.  Modern US fighter aircraft do not use RATs.  Even older aircraft like the F-16 elected to use an EPU vice RAT.  Neither the Super Hornet, nor other late Gen 4/Gen 5 aircraft use them.

Its also worth noting that modern electrical systems are so reliable you're probably more likely to inadvertently kill both engines and eject than you are to totally lose all power because of a system failure.

@SHAF "Wikipedia is often wrong". True but you're asking us to take your unsourced word against the unsourced word of a whole community. There's at least some chance that the unsourced Wikipedia article has been checked by people who've deleted stuff they know to be wrong. Your unsourced post certainly hasn't had that and, given that choice, I'll take Wikipedia any day of the week.

Using Google I found http://www.f-16.net/forum/viewtopic.php?t=1056 which suggests that the F16 doesn't have a RAT, but also http://www.airframer.com/direct_detail.html?company=121760 which suggests the F18 does have a RAT (but, who knows, maybe that's to power radar or something, not for emergency power).

@ChrisW The Growler has RATs to power its pods, but the Super itself, E/F/G models, relies on windmilling the engine to provide backup HYD when the engine dies.  I'm not sure about the legacy models.

@DavidRicherby I fly the Rhino.

It'd be helpful if you could address the idea of the aircraft "falling out of the sky." It obviously won't stop dead in the air and stop plummeting - I assume after some time (seconds? minutes?) without control it would stall, and then start plummeting

@raptortech97 Once the computers turn off its a crap shoot. Best case, you become a glider in the direction you were flying. Worst case, the computers died when the controls surfaces were weird and you instantly depart.  In the rhino, the batteries only give 5-10min of flight time (dependent on aircraft configuration and systems powered that drain the battery) if everything else is dead.

Define "modern". The A-10 is only 38 years old, is still in service and is expected to remain so until at least 2020 (its planned replacement, along with many other current service aircraft including the F-15E, F-16 and F/A-18, is the much-maligned F-35 program). It has redundant hydraulic systems for all major control surfaces, plus a set of drect cable linkages, so even in a fully unpowered glide a true "dead stick" landing is possible. However, this is probably an unfair example as the A-10 was designed in part for extreme survivability in low-altitude combat conditions where the aircraft could encounter practically everything that airplanes and their pilots don't like, from small-arms fire and flak to short-range ground or air missiles and even a well-aimed tank or artillery round.
"Modern" fly-by-wire jets typically have similar redundancy, but with no direct mechanical link from stick to control surfaces, they are at least partially dependent on electrical power for the flight control computer (in addition to the power required for the hydraulic motors). In the case of a total loss of electrical power, you're right, the aircraft would be uncontrollable until one of two things happened; the pilot got one of the electrical sources back online (typically an engine-powered generator), or he gave up and punched out.
One might wonder how much has to go wrong for the generator coupled to each engine turbine and the APU to fail, leaving the pilot with only battery power for the displays (and to attempt maybe one engine restart). The answer is "a lot"; the most likely scenario causing a simultaneous failure of all generation systems is a missile impact, and in that scenario most fighters wouldn't make it back anyway. However, a failure in the power distribution system of the aircraft might be more likely; this system is redundant as well, but there are some necessary bottlenecks, and one or two relatively minor failures in series could conceivably disable a plane mid-flight.

Only 25 years old? According to Wikipedia, it was introduced in 1977. That makes it 38 years old!

Damn my mental arithmetic. Editing...

To be perfectly fair, depending on your point of view, the A-10s flying now are only 10 years old at the oldest; the A-10C was first flown in 2005, and is arrived at via a combination of the A-10 SLEP replacing the wings and other fatigued airframe members of older A-10As, plus the PEUP program to upgrade the avionics to a glass cockpit with the capability to fire the latest GPS-guided munitions. Despite the cockpit upgrade, the A-10s retain their triple-redundant flight linkages.

When being attacked by an A-10 a tanker can greatly improve his chances of survival by standing up in the open turret hatch and flipping the bird at the incoming A-10. This may cause the pilot to laugh so hard he'll twitch the stick a bit and miss the target... Oh, BTW, and in case you've forgotten - the F-35 is The Answer. The only question is, to which question..?

Running out of fuel would seem to do the trick, as well.  Can't run the engines or the APU without it...

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text:
What could cause instant nausea when entering larger passenger planes?
This may not be the right forum for this question, but I almost always experience temporary nausea when entering the cabin of a larger passenger plane (e.g. A320). It hits me as soon as I enter the cabin and can be quite debilitating. Strangely enough it tends to dissipate almost completely after about 5 minutes inside the cabin.
Does anyone know what might be causing this? My only thought is that is has to do with the air inside the cabin as even the smell of the cabin when boarding (but still on the boarding ramp) causes the nausea to occur.
Additionally, I'm open to any suggestions for how to reduce this effect... I fly quite often and have learned to put it up with this sensation but I would greatly appreciate not having to go through this anymore.

It sound psychosomatic in nature.

Did you by chance smell something that smells like dirty feet when boarding the aircraft.  If so this could be the engine oil entering the bleed system of the engine and into the cabin.  There have been issues with these fumes incapacitating  crew members.  There has been a lot of talk about this on the Aviation Herald even today.

@DLH I wouldn't describe the smell as dirty feet but it does smell like exhaust almost. this smell has been exactly the same for every flight I've ever been on (300+ flights)

There are a few things that could be causing it but chances are its not the aircraft. When on the ground, with the engines off, aircraft simply have exterior air circulating through them. In the hot weather they are often connected to an external AC unit similarly in the cold weather they are connected to a heater. Cabin smells tend to vary widely and I cant find any data other than anecdotal evidence about how they are controlled and if they are quantified.
Once the engines have started they can use bleed air but if your symptoms are calm after 5 minutes its likely they are still using ground fed air at that point.
You may be experiencing light symptoms of Claustrophobia upon knowing you are entering a small, enclosed space. Some evidence points to the fact this can be cured with repeated exposure so the more you fly you may notice the effects reduced.

I would hesitate to call it claustrophobia. I've flown probably 300+ times in my life and never really felt cramped and claustrophobic. If it helps at all the smell reminds me of exhaust almost. It's been the same smell across all aircraft that's triggered this nausea.

On A320 and most of the airlines (exception for B787 and A350), the air conditioning is taking is air from the bleed system (ATA 36), which is furnish either by the APU, the engines or a ground system. When you are at the gate, only the ground system or the APU is providing air, but it may occurs that some residue of engine oil are inside the system and it can smell weird. Also, if the aircraft is old, the air conditioning system is really difficult to clean, so you will have that smelly air like in old house.
For the nausea point of view, it will depend of the person. I know there is some trials against Airbus and Boeing on that subject, it may be the case, but so far nothing has been decided.

From what it smells like, it could very well be engine oil. Its just odd that it's been the exact same smell across all aircraft for as long as I can remember.

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What are the legal effects of an inoperative anti-collision light?
In an airplane which is only equipped with a beacon for anticollision lights (1967 Piper Cherokee, for this example), what is the effect of an inoperative beacon?  Obviously, per part 91.205, anticollision lights are required equipment for VFR Night.  But, since the aircraft was certificated before 1996, it is not required under 91.205 for VFR Day.
Now, the interesting part is, under 91.209, since the aircraft was equipped with anticollision lights, it sounds like the aircraft would not be airworthy.
The guidance I've heard on this seems to be conflicting.  One argument was since the equipment was disabled and placarded, it doesn't qualify.  Alternatively, in 91.213(d)(2)(iii) (also referenced by AC 97-61 figure 2), it states that if the equipment is required by part 91 FARs, (91.209 seems to apply here), it is unairworthy (and deactivating/placarding is not an option).
A final point of confusion, specific to this in example: the beacon was an optional feature of the 1967 Cherokee according to the manual... which brings me here: any other opinions, short of a more formal clarification? I'm inclined to err on the side of caution, especially since the definition of "equipped" isn't getting any clearer (other than seeing that little red light on there and the "inop" marking on the panel).

The answer to your question is in FAR 91.205:
91.205(b) - Visual-flight rules (day):

(11) For small civil airplanes certificated after March 11, 1996, in accordance with part 23 of this chapter, an approved aviation red or aviation white anticollision light system. In the event of failure of any light of the anticollision light system, operation of the aircraft may continue to a location where repairs or replacement can be made.

and 91.205(c) - Visual-flight rules (night):

(3) An approved aviation red or aviation white anticollision light system on all U.S.-registered civil aircraft.  (it goes on to talk about color, which I've cut out) In the event of failure of any light of the anticollision light system, operations with the aircraft may be continued to a stop where repairs or replacement can be made.

So as you surmised in your question, a 1967 Cherokee is required to have an operating anti-collision light for Night-VFR operations (because the night anti-collision requirement is retroactive and doesn't care about certification date), but not for day Day-VFR operations (because it was certificated prior to 1996).

If you HAVE an anti-collision light it is required to be operating subject to FAR 91.213. The relevant part of that regulation says that you can take off with inoperative equipment provided that equipment is not:

(i) Part of the VFR-day type certification instruments and equipment prescribed in the applicable airworthiness regulations under which the aircraft was type certificated

You're OK for Day VFR because CAR3 (and FAR 23 prior to 1996) didn't require an anti-collision light for daytime operations.

(ii) Indicated as required on the aircraft's equipment list, or on the Kinds of Operations Equipment List for the kind of flight operation being conducted;

Your Cherokee predates the concept of a Kinds of Operations Equipment List in small aircraft by several decades, so your reference is 91.205.

(iii) Required by §91.205 or any other rule of this part for the specific kind of flight operation being conducted;

If the kind of flight is "Day VFR" the anti-collision light is not required by 91.205, but if you want to fly at night it is required (as we determined previously from 91.205).

(iv) Required to be operational by an airworthiness directive

No such Airworthiness Directive exists for anti-collision lights on the PA-28 family.
…so per 91.213 you can placard the beacon switch INOP and "deactivate" the anti-collision light (simply putting a bit of masking tape on the switch holding it in the off position & writing INOP on that is generally considered adequate) and fly in Day-VFR conditions (ideally to an airport where you can get a replacement lamp for your beacon).
Note that the fact that your beacon was optional equipment doesn't enter into the decision tree for 91.213: Any installed equipment gets evaluated according to this regulation. As an example my (1965) Cherokee has both a tail beacon (originally installed by Piper) and a belly strobe (added by someone over the years): if either is inoperative it needs to be "deactivated and placarded" appropriately.

Well, whoever said flying was easy...

@Radu094 Flying is easy. Landing is hard. Comprehending the regulations is impossible.

Yeah, the confusion comes in because as you mention, 91.213(d)(2)(iii) says "or any other rule of this part" and 91.209(b) requires lighting it if "equipped."  Still, thank you for the extremely thoughtful answer!

@dougk_ff7 Ah, I forgot about 91.209(b) - That could be interpreted to require you to have a working anti-collision light if the aircraft is equipped with one (same logic as 91.209 - optional or added later doesn't matter) unless "If because of operating conditions, it would be in the interest of safety to turn the lights off". (See what I mean about "Comprehending the regulations is impossible"? Everything is in at least 3 places :-P)

@dougk_ff7 & voretaq7 Does anybody want to volunteer to ask the FAA for clarification? 91.209(a) deals with lighting requirements during nighttime operations (or what passes for such in the Alaskan summer). This leads me to think that 91.209(b) is primarly intended to explicitly allow pilots to switch off the anticollision strobe lights during nighttime operations on taxiways and ramps (where they could blind other pilots), and in IMC conditions (where they can be disorienting).

91.205 is a red herring here. 91.209(b) is applicable:

[No person may:] Operate an aircraft that is equipped with an anticollision light system, unless it has lighted anticollision lights. However, the anticollision lights need not be lighted when the pilot-in-command determines that, because of operating conditions, it would be in the interest of safety to turn the lights off.

You are equipped with anticollision lights. So flying without them lit is illegal.
It is not required equipment under 91.205 or the original certification. So as long as it has not been subsequently required by an airworthiness directives or an STC or something, you could decide to remove it from the airplane. In that case, you would no longer be equipped with anticollision lights and you would be legal to fly.
The FAA touches on related topics in this legal interpretation. It references 91.209(b) in stating that a 172 with operative strobes but an inoperative beacon is not airworthy, regardless of the certification date of the 172:

Accordingly, operation of an aircraft using only the aircraft's strobe lights after placarding its red rotating beacon as inoperative and making an entry in the aircraft logbook would not be permitted unless such action is authorized by a waiver.

A working anti collision light is not required for the 1967 Cherokee because the key statement in 95.205b11 is for aircraft certificated in accordance with FAR part 23.  A Piper Cherokee  was certified under CAR (civil aviation regulations) part 3, not FAR part 23 (See TCDS 2A13). Therefore this sub paragraph does not apply to that aircraft. If, and only if, this aircraft is operated at night (as specified in 91.209 the light would be required...but not for Day VFR.

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61.41 as a general aviator can I log training time I get from military instructors both in Military and general aviation aircrafts
When I am receiving flight instruction from a military flight instructor in a military aircraft and I am not a military pilot (just have a private pilot certificate) and the instructor endorses my logbook to show training given is that allowed? Is this allowed per 61.41 sine the instructor is in a program designed to train pilots?

@757toga, I would tend to agree, but I had already drafted an answer that addresses the shortcomings in the question.

@757toga, 61.41 is beneficial for those who may not complete military flight training and be properly designated.  In such a case you can still apply the hours towards FAA ratings, the difference is you would need to pass a checkride with a DPE vs taking the written MilComp exam.

The military flight instructors are in a program specifically designated to train pilots. The regulation states that the instructor has to be in the program. It doesn’t say anything about the student. Can I have military instructors endorse my logbook showing training given when I flying a military aircraft and I’m not a military pilot, I just have a PPC

I am in the military.

James, I'm not an English major to be able to break down the sentence in the regs, but it certainly does not exclude the student from the requirement to be a part of the same training program as the instructor. Because if you remove the phrase about the instructor, (prepositional phrase?) it still makes sense grammatically: "A person may credit flight training toward the requirements of a pilot certificate or rating issued under this part if that person received the training in a program for training military pilots..." And it would seem apparent that is the intent.

If you are able to observe flight instruction, (per your earlier question) and swap into a pilot seat then I presume you are a crewmember on either a helicopter or transport aircraft. It's a great opportunity to observe crew coordination and get a little stick time,  (been there, done that...) but unfortunately I don't see a way to legally log it in your personal log book with your private pilot time.

I was curious I just log PIC time.

So, do you have a type rating in the aircraft?  What is it you fly?  (You seem to be intentionally vague...)

The aircraft doesn’t have a type rating? The aircraft is a c17. What specific question do you have?

The FAA requires that you have a type rating for large turbine powered aircraft. The military doesn’t use the same term, but obviously requires equivalent training and qualifications.  You asked if you could log it as a “general aviator” which I presume meant your GA logbook, but if you aren’t qualified in the aircraft to be legit to log PIC time in your military logbook, what makes you think the FAA would accept the time?

P.S.  If you don’t like my answer or comments I suggest you edit your question to add details about you being a qualified crewmember, (but not qualified pilot) on the C17.  I will vote to reopen and we can see what others may have to say.  Happy to make those edits for you…

As you are aware, 61.41 allows you log military training but only as long as you are "in a program".

(a) A person may credit flight training toward the requirements of a
pilot certificate or rating issued under this part, if that person
received the training from:
(1) A flight instructor of an Armed Force in a program for
training military pilots of either the United States or...

Whether or not your military flight instructors have FAA Flight Instructor Certificates is irrelevant as long as they are qualified by the military to teach you in the aircraft that you are flying, AND you are in a program for training military pilots.
If your friends are not FAA CFIs then they cannot give flight instruction in general aviation aircraft outside the military.
If they are, then they can.
It's really that simple, but you cannot randomly mix and match military and FAA flight instructor qualifications as your question seems to suggest.


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What was the reason for my flight’s low cruise altitude?
I’m a fairly new aviation enthusiast and am just curious to know the answer to this question. I flew Boston to Newark yesterday 14/6/22 (UA2396) and we cruised at or under 16000 feet for the whole flight. It’s only a short route but when I have flown the route previously we cruised at around 20-24000. The flight was delayed and Newark had a delay system in place too (not sure what that means), so wondered if that was relevant? It felt strange to fly at what felt like a much lower altitude than normal! Thanks for any comments.

Another consideration is the altitude between 18 and 25000 ft is chockablock full of turboprops flying way slower, causing ATC traffic integration issues, so the choice is sometimes stay under or go above the turboprop layer.  The fuel burn will be brutal at 16k with turbofans, so you would never do that on trips of any length unless you really really had to.

Does this answer your question? Why cruise at 7000' in an A319?

This is typical for short hops. High cruise altitudes are good for fuel efficiency and to get a higher speed over the ground. However, it takes a lot of fuel to get to 30,000ft and it may take more fuel and time to get up to that altitude than would be saved cruising at that altitude given the short distance.
Another consideration is wind speed. Think of wind as a river, if you swim upstream it slows your progress down even though the speed through the water is the same. The prevailing wind goes from west to east, which means your flight was probably into the wind. If the wind speed was especially high the flight may have taken a lower cruising altitude for more favorable winds.


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Why did the US adapt the AIM-9X and not the ASRAAM IR missile?
I was looking and saw that the British developed a missile called the ASRAAM, which was not adopted by the United States. Why? Also, how do the AIM-9X and ASRAAM compare? In which situation would one be better than the other?

What has your research shown? It is sort of a new and improved AIM-9.

So far, it has said the ASRAAM is better, but the answers all seem like random British people who want to one-up America in as many ways as they can. About the actual capability, I can't decide, as the AIM-9X can pull harder g turns, both have a Lock on after launch capability, and the ASRAAM is harder to jam. I also figured the AIM-9X be better in some ways since the USAF chose the AIM-9X. If the ASRAAM were better in all ways, they would have modified their planes to carry the ASRAAM.

The reasons are not always technical: "While ASRAAM was entering production, momentum behind US-led industrial and political lobbying grew significantly and, combined with the strengthening European economy, forced the US government to conclude testing in June 1996 and move away from the ASRAAM program." (from https://en.wikipedia.org/wiki/Asraam)

Performance of military weapons is off-topic here.

@Bianfable why exactly though? Because of subjectivity of the questions or rather because of the topic in General? We had some similar questions in the past right?

@U_flow Should missiles be on-topic?

Exactly, that meta exchange has 7 counter AND 7 pro votes. Obviously the community is divided (50 50 as it seems). Nevertheless there is as much vote to keep missile related questions on topic as off topic, making the Statement that missiles are off topic false. That being said, the questions is interesting from a system point of view

The USA has always looked internally for weapons development and purchasing. It's extremely rare for the US military to buy anything from another country, even if it may be better. It's about politics, not best.

I'm voting to close this as opinion based. Which is better is subjective.

This is not a subjective question. The USA evaluated this missile, and deliberately announced their decision to not adapt this missile. Therefore this is not subjective. The discussion which are the exact reasons for this rejection, is speculative. However this question is perfectly valid.

@JustACoder might I propose to rephrase the title of the questions into an actual questions? Perhaps: Why did the US adapt the AIM-9X and not the ASRAAM IR missile? You can then divide the questions further in the questions body.

Sure, I did it.

Three vaguely related questions.

Why was the ASRAAM not adopted by the USA? Officially the ASRAAM was evaluated in the context of tender. The entries were the AIM-9X Sidewinder and the ASRAAM. However it was rejected as a result of tests conducted during that evaluation (link). Therefore, simple as that, the missile was evaluated and found to be not satisfactory, or less satisfactory then its competition (the AIM-9X).
I could however not find a source citing if explicit reasons where given. However a lot of speculation emerged if this decision was based on factual reasons such that the ASRAAM could not be deployed on aircraft carriers, does have unsatisfactory turning performance shortly after firing or if the sidewinder simply had more value because exisiting motor sections could be reused (apparently 20.000 of these sections were still around and could be reused). Other reasons could include political considerations: Perhaps the USA did not want to buy "foreign" material. But again, that is speculative.
Which of the two missiles is better? This very much depends on requirements. Both missiles use the same Hughes IR Seeker (a focal plane imaging array seeker). Both have a very similar combat deployment scenario: That of a short-range engagment. The key differences are:

The ASRAAM has higher range due to less aerodynamic drag and a bigger motor
The AIM-9X is better at initial turning rate which offers an advantage shortly after the missile leaves the launch rail.
The AIM-9X has a smaller diameter (127mm vs 166mm) therefore less space for warhead, motor etc.
The warhead of the AIM-9X is a bit smaller, therefore less lethal
There are differences in how both missiles compute their guidance solution in response to flares, resulting in differences in performance in this respect. The exact differences are classified

However interesting to note is that both missiles acquired some upgrade in order to counter these points: The AIM-9x was upgraded in the Block III variant to improve its range (and also to gain a lock-after-launch capability), while it was apparently important for BAE to issue an upgrade for the ASRAAM which enables it to hit targets behind the aircraft (also coupled with lock-after-launch capability).


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Holding position marking/signs

I thought that ILS holding positions marking are used only on taxiway but this runway seem to have them too.
What is the usecase of using both the standard holding position marking(here yellow with 4 lines) and the intermediate holding position(here red, ladder type) ?
Is the red line an ILS sign in this case next to the marking?
Cannot find any reference on using the ILS on runways in the FAA specification.
Image details:
Runway 4R-22L on O'Haare Chicago Airport.
Coordinate: 41.96690186, -87.88337077


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What are my take off minimums?
Requesting for some clarification.
Part 91 operator. 0-0 visibility and ceiling minimums
Departing Rwy 15 at ADS
Can I depart with a standard 200 ft/nm cross DER 35 ft. since I don't need to comply with the 400-2 1/2 wx? (0-0 ...right?)
or
Do I fall under the std.(which from what I understand, is ...0-0?) w/ min. climb of 325' per NM to 1100?

I would never take off from someplace where I couldn't land in case there was some problem. 0-0 visibility would keep me on the ground until it cleared up some.

You are incorrect in your understanding of standard. According to

§91.175   Takeoff and landing under IFR. (f) (2) (i) For aircraft, other than helicopters, having two engines or less—1 statute mile
  visibility. (ii) For aircraft having more than two engines— 1⁄2
  statute mile visibility.

However, these minimums do not apply to you because just before the definition of standard it says:

(f) Civil airport takeoff minimums. This paragraph applies to persons
  operating an aircraft under part 121, 125, 129, or 135 of this
  chapter.

So standard minimums are 1 statute mile for 1 and 2 engine aircraft and 1/2 statute mile for more than two engines but the rule doesn’t apply to you since you are flying under Part 91.
The next part of that section says:

(3) Except as provided in paragraph (f)(4) of this section, no pilot
  may takeoff under IFR from a civil airport having published obstacle
  departure procedures (ODPs) under part 97 of this chapter for the
  takeoff runway to be used, unless the pilot uses such ODPs or an
  alternative procedure or route assigned by air traffic control.

In this case, since there is a published ODP, you are required to have either the visibility or the climb performance. If you can climb at 325' per nm to 1100' then you can take off in 0/0 conditions.

What about the 400-2 1/2 wx? is that a minimum climb of 200ft/nm?

@RAU The visibility minimums are there so you don’t hit something that you can’t see. Presumably you’ll be able to see the obstacle and maneuver around it. So a climb rate of 200 ft/nm would be fine. If there is rising terrain that requires a climb rate of more than standard, then you would have a notation that requires a specific climb rate.

I thought F(3) does not apply to part 91?
"(f) Civil airport takeoff minimums. This paragraph applies to persons operating an aircraft under part 121, 125, 129, or 135 of this chapter."

@RAU Exactly. The definition of standard takeoff minimums is the same for  everyone. But only categories listed in (f) (3) need to comply with the minimums defined in (f) (2) (i).

Im sorry, still having a hard time wrapping my head around this. So I can actually depart with 200 ft/nm climb since part 91 does not need a 400-2 1/2 wx minimum?

@RAU You have two choices listed on the departure procedure. You can depart with 400 and 2 1/2 and 200 ft/nm with 35' above the departure end of the runway OR you can depart with 0/0 visibility (since you are Part 91) and 325' per NM up to 1100' .

Understood, thank you so much for the clarification!

What this tells me is that I can take off with any legal visibility/ceiling for my type of operation if I can maintain 325’ per nm climb. If I can only accomplish the standard 200’ per nm climb, I need 400’ ceilings and 2.5 miles of visibility, regardless of operation type.
Essentially it’s saying that there’s something out there that you’ll hit if you can’t maintain the 325’ per nm climb gradient. If you can, great, go. If not, you need the increased visibility to see and avoid it.


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Significance of "weather conditions less than the minimums prescribed for VFR flight"
"weather conditions less than the minimums prescribed for VFR flight" has repeatedly come up in FAR chapters pertaining to IFR.
One example is 61.3 (e):

No person may act as pilot in command of a civil aircraft under IFR or in weather conditions less than the minimums prescribed for VFR flight ...

Why does it specify IFR and "in weather conditions less than the minimums prescribed for VFR flight" separately? Doesn't IFR cover all "in weather conditions less than the minimums prescribed for VFR flight" cases (though I know that the reverse is not necessarily true)? So what's the significance of a separate clause for "in weather conditions less than the minimums prescribed for VFR flight"?
Clarify my question:
Yes, I understand that IFR can occur in either VMC or IMC. But my question is shouldn't all IMC happen under IFR (at least legally)?

Comments are not for extended discussion; this conversation has been moved to chat.

Doesn't IFR cover all "in weather conditions less than the minimums prescribed for VFR flight" cases (though I know that the reverse is not necessarily true)?

As your question astutely implies, the fact that IFR flight may be conducted in VMC is irrelevant to the interpretation of the regulation.
The regulation would clearly apply to all IFR flight even if the clause about "or in weather conditions less than the minimums prescribed for VFR flight" had been omitted.
So the clause is not needed to account for the possibility of IFR flight in VMC conditions.
The clause about "or in weather conditions less than the minimums prescribed for VFR flight" (key word "or", not "and") expands the scope of the regulation to include pilots illegally flying under Visual Flight Rules in inadequate weather conditions. No other pilots would be included by this clause, who would not already have been included by the regulation as it would read had the clause been omitted.
Either the FAA didn't think this one through very clearly, or they thought it appropriate to have the regulation be broad enough to impose an additional violation, upon pilots who were already violating other regulations, by illegally flying VFR in inadequate weather conditions.


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Which aircraft did I photograph at ZRH?
I took a couple of pictures of various aircraft and I would like to know which aircraft I photographed. I have no idea, expect that all of them took off from ZRH and should be commercial airliners:

Beautiful pictures :)

Just wanted to point out that the plural of "aircraft" is "aircraft". :)

If you can read the immatriculation (at the rear of the aircraft), you may searh on airliners.net

One of the simplest things you can do is to type in the registration into Google which will normally give you results of the type and history of the aircraft.
Otherwise, many airlines don't operate too many types of aircraft so a quick look on Wikipedia and looking through 'fleet' should show you which types it may be, from which elimination should be pretty quick.
The registration is normally visible on the back of the fuselage and under the wing (D-ABEP on the rear fuselage below), and the last two letters are (often) printed on the aircraft 'forehead' above the cockpit windows, the top of the tail and the nose gear doors (EP on the nose gear doors below).

Aircraft from your photos:

Boeing 737
Airbus A320
RJ85
Airbus A320
Airbus A321
Fokker 100

Ok, but how do I know the registration?

@RoflcoptrException That's the little code on the back of the aircraft fuselage :) (And the last two letters are displayed on the nosegear doors)

Cool, thanks a lot!

@RoflcoptrException: Note also that you can determine the registration country of the aircraft from the code. If it starts with N it is USA, C is Canada, G is the UK, D is Germany, and so on.

And sometimes part of it is shown on the top of the vertical stabiliser as well, and/or on other places (e.g. KLM tends to put the last 2 letters over the windscreen rather than the nose gear bay doors).

The accepted answer has good advice. I would add that a quick and easy way to make a guess at the manufacturer is to look at the ends of the wings. Notice how in the first picture the wings "bend up" at the end. This is highly characteristic of Boeing 737s.
By contrast, the "fence" style wing tip that you see in three of your photos is highly characteristic of Airbus.
See Wikipedia's article on the matter for more information about why wings have unusual tips.

Blended winglets are no longer unique to Boeing. I've started seeing Airbus's "Sharklets" in the wild.


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What is this molten metal coming from the engine of an Avro RJ 100?
Yesterday I flew in an Swiss Avro RJ100. As soon as we landed I was shocked to see some sort of molten metal which was incandescent and glowing red dripping down from the vent as indicated in the picture. It was almost catching fire! I was suprised to see immediately the maintenance van pitch up to the plane when we didn't even get to a stop. Is this normal?
This image isn't of the problem flight, but shows where the problem was.

No its not normal. It sounds like an oil leak that burned thought the engine cover. They must have shut down the engine in flight, but unless you hear the engine fault like a compressor noise you wouldn't notice it was shut sown. --  link to incidents reagarding the RJ's -- http://www.aeroinside.com/incidents/type/rj1h/air-avroliner-rj-100

Interesting site! The plane is probably the same one that had the engine shutdown HB-IXR as it had that livery and it is the only RJ100 that has it in the fleet. Probably something is still wrong!

@FabrizioMazzoni I don't know about Jul 2014, but two years later (Oct 2014) HB-IXR certainly isn't the only RJ100 in Swiss fleet. They have HB-IYY as well, if not more.

I do not see anything in your photo, apart the engine that looks perfectly normal.
Anyway
here it is written that the fuel burns at up to 2000 degrees Celsius and the temperature at which metals in this part of the engine start to melt is 1300 degrees Celsius. Hence the metal may melt if something goes wrong.
Avro RJ100 has four engines so should be able to land with one inoperative. From the question I have just asked myself, it will not be qualified as accident so may not get widely known.

The picture is not one I took. I just checked on the internet to show where the problem was.

The incident most likely will/did get reported. Date and flight number or aircraft registration would be need it to find it though as there are hundreds of incidents reported and published every day.

Looking at your photo, it seems the sun is shining roughly from your two o'clock.
What you saw may not have been metal, but simply some other fluid (fuel, lubricant, hydraulic) leaking out of the engine, reflecting the sunlight.

It's not actually his photo-- ps I guess that information wasn't obvious from the original post until a recent edit

it seems that what you were looking is one of the reverse thrust latches that wasn't properly secured.


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What type/model of plane is this?

I came across this photo but it doesn't have any other info. What type of plane is it? Also, is it some sort of seaplane perhaps? I say seaplane because it was tagged with the word "seaplane". Seems Cessna-ish to me but I'm clueless beyond that. Is it possible to identify the exact model?

It looks like a Cessna 208 Caravan to me:

These are single-engine high-wing turboprops, useful for a variety of cargo and passenger-hauling tasks. Here's what a 208 in seaplane configuration looks like on the outside:

Your photo looks like an older plane with the original radio stack and no glass, unlike these newer cockpits. In addition, somewhat startlingly, the right-hand control column and yoke have been removed, but they bothered to keep the copilot's 6-pack. That's odd, from my sensibilities, and it tells me the plane was altered in the cheapest possible way for use as a pure short-range passenger ferry. The right-hand seat can now accomodate an extra passenger (and becomes the best in the house for enjoying the view), without the possibility of that non-flier binding up the pilot's controls.

Would they be removed if it's used for "tourists"?

See my edit; I thought of that after I posted the original. Still somewhat odd, though more sensible if the pilot is spending his days taking groups of people on pleasure hops around a lagoon or bay. The front seat is now an extra paying passenger who can't inadvertently bind you up while twisting around his seat to get pictures. Doesn't appear to be illegal, but it limits the utility of the plane for tasks beyond air tours.

I did find the photo posted by a tourist I think.  So curious how you narrowed down which Cessna it was? ☺

I took a guess (I agreed it'd likely be a Cessna, as most seaplanes are high-wing), and searched Google Images for "Cessna Seaplane cockpit", then scanned that for images with similar panel configurations on the copilot side, and found a few definitively identified as the 208. A slightly wider search of similarly-sized models shows that 6-pack on the copilot's side to be a pretty dead giveaway; most other 100s and 200s have a pretty spartan right-hand panel, while the panels for twins in the 300/400 levels tend to have a more beveled corner (and many more gauges for multi-engine monitoring).

Can it land in water?

Of course; those big long hull sections under the fuselage in that last picture aren't for decoration.

Lol, I don't know how I missed that!


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Is it permitted to fly a 737-800 with one pilot?
A 737-800 was scheduled to leave from a Canadian airport to Mexico, but was delayed: the airline said the reason was that one of the pilots called in sick.  As a workaround, the airline flew the plane to a nearby Canadian airport (1:44 flight time) to pick up a new pilot, then flew directly to the Mexican destination.
My question: do regulations permit flying a 737-800 with passengers for that distance (1:44) with only one pilot under these circumstances?

It’s more likely that they had another pilot which couldn’t do the whole flight but was still able to do the shorter flight. Definitely wouldn’t have taken off with a single pilot.

1:44 = 1h and 44min?

@jcaron It is even possible that the airline gave vague information because what they were actually doing was to rearrange the pilots available among different flights.

@user2705196 Yes, that's a normal way to write 1 hour and 44 minutes in North America. (It's also a normal way to write 1 minute and 44 seconds, but I think it's safe to assume that the flight wasn't quite that short. :) Context generally makes it apparent which meaning was intended or else a different format is employed.)

Unless there is an exemption I am unaware of, the 737-800 always requires a pilot and co-pilot.
Perhaps you misunderstood? Longer haul operations require three (or more) pilots, so maybe the shorter flight had two pilots and they were going to pick up a third?

This seems like a good guess, but I'm struggling to imagine which route from Canada to Mexico would require an augmented crew. Flights from Vancouver or Edmonton to Cancun max out at around 6 hours. I suppose its possible there was a situation where a crew only had a couple hours left in their duty day, so they were assigned to fly the aircraft to another airport where a fresh crew could continue the flight.

@Zach It's also possible that a pilot was available for a 4 hour period or so needed to accompany the otherwise single pilot to the close-by destination and take the next flight back; but s/he was not available for the long haul, due to rest requirements or a subsequent short haul.

@Peter-ReinstateMonica this explanation seems most likely - scheduling meant they had another pilot who could fly, but only to the nearby airport. They land, swap pilots, and take off again.

Flight time between the original Canadian city and the Mexico destination is 5-6 hours

@GlennLane Probably not this, then, unless Air Canada has some specific policy requiring an augmented crew sometimes when it's not required by law. The exact reason can only be speculation, but I stand by the main idea that it is very, very, very unlikely they dispatched a 737 with only 1 pilot, and there could be any number of reasons they needed to swap out pilots after a brief detour.

In addition to the possibility of one of the pilots on hand at the airport having flown enough in the past day that they could legally fly a 2 hour flight but not a longer flight, there may be other issues. While I would expect most pilots in Canada (and indeed around the world) to have passports and other documentation as needed to fly anywhere that their airline flies, it is certainly possible that a qualified pilot did not have their passport available for some reason (lost, stolen, forgotten, expired) and was therefore limited to domestic flights. They could fly between Canadian airports but not out of the country.

Another possibility is that their available 2nd pilot was over 65, and therefore ineligible to fly over US airspace. Canada doesn't have mandatory retirement for pilots, but US does. Especially during a pilot shortage, Canadian airlines will accommodate them on flights within Canadian airspace only, sometimes even taking irregular/inefficient routes instead of cancelling.
https://torontosun.com/news/national/arbitrator-air-canada-pilots-cant-fly-past-the-age-of-65

Your linked article directly contradicts your answer. Your article says Air Canada has a 65 year old limit, and such a limit was upheld legally. Is there something else you wanted to post?

@user71659 It says that Air Canada has a 65-year-old limit because of the need to fly frequently into the U.S., but that Canada itself (i.e. Transport Canada) does not have such a rule. While Air Canada is the largest airline in Canada, there are several others that also operate flights to the U.S. and Mexico (e.g. WestJet, Flair, Swoop, etc.)

@reirab Correct. Would add that Air Canada’s own rules in 2020&2021 (when they wanted every excuse available to fire people due to low demand) may have changed in 2022 when they can’t find enough pilots (due to forced and unforced retirements and high global demand for pilots, especially when Air Canada pays less than many major foreign carriers).


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What is the purpose of a freewheeling unit in an helicopter, if a centrifugal clutch is already present?
Some helicopters such as the Bell 47 are fitted with a centrifugal clutch.
Centrifugal clutch will engage only at certain engine RPM. If the engine fails, the engine RPM will reduce and the centrifugal clutch will disengage the rotor from the engine. So, why is an additional freewheeling unit needed?

You should edit your question to highlight a link with aviation.

@ManuH - I am new to SE. The original question was in relation to Helicopters. So, I added that.

if you have an example of a model that is fitted with such device, you should put it as an example

@ManuH: My question is specifically related to the need for a freewheeling unit in helicopter. Not as a standalone device.

Feel free to edit your question again to add precision if feedback make you think there is still blur areas.

the centrifugal clutch will only disengage after its rotating speed falls to the disengagement point. The over-running clutch disengages the engine from the rotor at the very instant that the engine's rpm falls below that of the rotor.
In this way, the rotor is never wasting kinetic energy by trying to turn over a dead engine and the vehicle stands a better chance of achieving successful autorotation.

Thanks for the answer. One query —  if the freeweeling unit is not present and the engine fails, then the output shaft of the engine will keep rotating for a few moments. For those few moments, it could contribute to the rotation of the rotor. So, that "decaying" power of the engine is getting wasted by disconnecting instantly. Where am I wrong in this thinking?

@Raj As long as the "downstream" inertia is still "helping" the rotor, the freewheeling unit will not disengage - the freewheeling unit will not disconnect instantly, only when the torque transfer reverses (rotor driving the engine instead of engine driving the rotor). So no energy is ever wasted by a (sprag clutch) freewheeling unit.

@Sanchises - understood. Thanks a lot for the clarification.

Helicopters may or may not have a centrifugal clutch which will provide drive to the rotors at an rpm just above engine idling, but all helicopters need a freewheel unit in case of an engine failure. The implications are best understood when considering a single engine helicopter. At the point the engine fails rotor rpm decay is very rapid. Within seconds, with no action taken the rotor rpm will decay to a point where it will become irrecoverable. The autorotative force (the turning element of autorotation) will be lost. To avoid this the collective control requires to be lowered to reduce pitch and hence rotor drag and the gearbox / rotor system needs to be disconnected from the engine immediately as this extra load would again inhibit the helicopters ability to enter autorotation.


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In helicopter's forward motion, how is the forward pitching moment taken care off?

When the rotor disk is in the position shown by the dashed lines, the net Lift is at an angle. It should produce a forward pitching moment about CG (Center of gravity). That can cause the helicopter nose to go down with a further increase in the moment angle and further pitching. What stops/controls this from happening in the actual scenario?

Welcome to Aviation Stack Exchange.  I made a small edit to clarify; you are welcome to roll it back if you don't feel it represents your intention for the question and clarifies it.  Just click on the "edited 1 minute ago)" (or whatever) tab to do that.

@quietflyer - thanks for the edit.

It's a complicated answer, with many contributing factors in a multi-dimensional matrix. In a helicopter flying at forward speed, there are several stabilising stability factors and several de-stabilising ones.

Before the helicopter can fly at speed, it needs to take off in a hover.

The rotor provides the lift force to climb.
Gravity applies down force in the Centre of Gravity.
The rotor hub is hinged - one could picture the fuselage as hanging off of the rotor hub, like a pendulum.

From this answer, own work
In this situation, hinging freely, the CoG would move directly underneath the rotor hub without re-aligning the rotor - the helicopter would stay in place, and only the fuselage would tilt until the CoG is underneath the lift vector. There is a range of allowable horizontal CoG positions, which would result in a range of fuselage angles when climbing up in a straight hover. Of course, if the CoG is chosen excessively forward or rearward, this scenario would result in an impossible fuselage angle.
But the rotor hub hinge does transfer torque, from rotor to the mast and vice versa. The fuselage is not free to dangle underneath the hub. From Prouty, Helicopter Performance, Stability and Control:, describing behaviour in a vacuum:

The teetering rotor in a vacuum has no tendency to align the rotor and mast perpendicular to each other, while the very common hinge offset rotor does. And in the atmosphere, the teetering rotor also wants to align the mast perpendicular tp itself via the torque of the flapping effect described here.
So a helicopter taking off in a hover with the rotor horizontal, aligns both the fuselage and the rotor until the CoG is underneath the lift vector. If the CoG was not exactly underneath the hub centre, the fuselage rotation tilts the lift vector and the helicopter starts to drift, which needs to be compensated by cyclic stick input from the pilot. From FAA Rotorcraft Flying Handbook, Chapter 7 Weight and Balance:

CG FORWARD OF FORWARD LIMIT. You can recognize this condition when coming to a hover following a vertical take-off. The helicopter will have a nose-low attitude, and you will need excessive rearward displacement of the cyclic control to maintain a hover in a no-wind condition.

Note that the above means that the rotor wants to align to the forward lean of the fuselage, which tendency must be compensated for by rearward cyclic.
In order to fly forward the pilot moves cyclic longitudinal forward, effectively tilting the rotor disk forward. As seen above, this also tilts the fuselage forward, moving the CoG to a new position further aft - this creates a nose-up moment, compensating for the nose-down moment of the thrust/drag torque.
When the helicopter picks up forward speed, air pushes at the fuselage: there is parasitic drag. This wants to tilt both the fuselage and the rotor further forward.

At increased airspeed, the rotor flapping provides an increased nose-up torque: the forward moving blade experiences higher lift at higher speed, and reaches a higher tip position when pointing forward. As explained in 2. above, this results in a fuselage nose-up moment as well due to the hinge coupling between rotor disk and fuselage.
The helicopter trim angle at speed can be further influenced by incorporating a horizontal tail, which applies a nose-up torque at speed. The horizontal tail incidence is often variable, in order to provide a wide range of stabilising moments at cruise speed, high angle descent etc.
The horizontal tail in cruise usually has a negative angle of attack, and is designed to make optimal use of the rotor downwash upon it. Horizontal tails are not required but highly desirable, for positive cyclic speed stability.
But a horizontal tail is ineffective in the hover, and a rotor on top has negative speed stability, as explained in this answer - the main reason for the instability in the hover of conventional helicopters, requiring constant stick inputs to maintain position.

Summarising, the nose-down pitching moment at forward speed is compensated by:

The flapping angle of the rotor disk.
The hinge moment coupling, either from hinge offset or from aerodynamic coupling in case of a teetering rotor. This effect wants to keep the rotor mast aligned perpendicular to the rotor.
The horizontal tail.
The useable horizontal range of CoG location.
And not mentioned above: in some cases canting of the tail rotor.

Thanks for the detailed answer. One query - in point 2, if I balance moment about the CG, then we get a counter-clockwise moment due to thrust vector. The moment due to drag is zero about CG as the drag vector is passing through CG point, so how does this compensate? or is it being compensated by the moment of Lift vector about CG, which turns out to be clockwise? (For this to happen, the resultant of Lift and thrust vectror will have to pass through CG)

The flapping is more "nose down" with speed, not nose up.  There is indeed a natural "flap back" as described in #4, but that is more than countered by forward longitudinal cyclic.  The end result is more nose down flapping and hub moment at high speed.  BTW the fuselage typically adds more nose down moment at high speed as well.

@Mat Yes the swash plate angle is more nose down with speed, selected by increased fwd cyclic longitudinal stick.

@RajArjit The rotor hinge moment mentioned in point 3. balances out a CoG not in line with the lift vector.

The main rotor often provides a pitch up moment about the CG, opposite to the diagram in the OP.  This is due to it being located at a smaller station line, forward of the CG (even after accounting for tilt).
The main rotor is flapped forward at speed, with its thrust tilted forward.  However, the vector is still often positioned and oriented to provide a nose up pitch moment about the CG.
The main rotor "hub moment" will indeed provide a nose down pitch moment.
The horizontal stabilizer on the tail will typically provide a large nose up pitch moment at speed.
See this link for such information.

If a helicopter is moving left, and I see a helicopter from the front, then the lift vector will provide a moment to rotate the helicopter counter-clockwise.

Main rotor thrust (including the aero forces over all blades) typically acts on a line in front of the CG, providing a nose up pitch moment.  The "hub moment" however is the moment the rotor creates about its own hub.  With the blades flapped down over the nose this hub moment provides a nose down pitch moment (assuming there's a flap spring or hub restraint).

Let's assume that the when the helicopter fuselage is horizontal (skids level), the CG is directly under the rotor mast.
For a torque problem, we are free to choose any arbitrary pivot point, at least when rotational acceleration is zero and G-load is one, so no additional apparent inertial force due to rotational acceleration or G-loading acts upon the CG.
If we want to figure out how things are balanced in a steady-state hover or steady-state cruising flight, it may simplify things to take the top of the rotor mast, rather than the CG of the helicopter, as the pivot point for the torque calculation.
Note that in this case, the tilt of the rotor disk and resulting offset thrustline exerts no torque about our chosen pivot point, but the drag vector of the fuselage--presumably acting near the CG of the fuselage-- does exert a torque about our chosen pivot point.  The two effects are interconnected-- in steady-state cruise, offsetting the drag vector is the only reason that the rotor disk must be tilted.
Assume for the moment that there is a completely rigid connection between the fuselage, rotor mast, and rotor disk.  In that case, if the rotor disk tips, the fuselage tips.  The rotor disk cannot tip relative to the fuselage.
Assume that the rotor itself has no mass.  Draw the vector triangle of R (rotor force), L (lift or upward component of rotor force), and T (thrust or forward component of rotor force), with right angles between T and L, and R as the vector sum of T and L.  Assume that the resulting net force R acts at the top of the motor mast and is pointing in exactly the same direction as the top of the rotor mast.
Assume all the mass and all the drag of the helicopter are concentrated at the CG of the fuselage.  Draw the vector triangle representing W (weight), D (drag), and F (net force generated by fuselage) with right angles between W and D, and with F as the vector sum of W and D.  This triangle must be a geometrically similar triangle to the previous one-- the one associated with the rotor.
This means that given all these assumptions, the net force F generated by the combination of Weight and Drag always is exactly in line with the rotor mast.  Thus no torque about the top of the rotor mast is generated by the combined effects of Weight and Drag.
Or to put it another way, the net force R generated by the rotor system is directly in line with the CG of the fuselage after all.
This also means that, given all these assumptions, even though in reality the helicopter disk system is free to pivot to some degree with respect to the helicopter fuselage, or vice versa, (see Why does the helicopter's nose go down when the cyclic is pressed forward (in a hover)? for more ), in steady-state cruising flight there is no inherent tendency for the fuselage to hang at a different angle from the rotor disk than it would it there were no flexibility in the connection between the fuselage, rotor mast, and rotor disk system.
Note that if there were some tendency for the fuselage to hang at some angle other than "square" to the rotor disk system in cruising flight, this would affect the position of the cyclic stick required to obtain any given net pitch torque (or lack thereof) from the rotor disk, just as tipping the rotor blade system forwards or aft when the helicopter is at rest on the ground changes the cyclic angle of one blade relative to another. For example, if the fuselage were for some reason hanging straight earthwards from the top of the rotor mast even in high-speed cruise, the (tilted) rotor blade system would be generating a nose-up pitch torque even with the cyclic stick centered.
One effect that could cause the fuselage to hang not "square" to the rotor disk, but rather somewhat closer to straight "down" toward the earth, would be if the drag vector acts above the CG of the fuselage.  This is likely often the case in reality.
This whole question is really all about whether the rotor blade system needs to generate a nose-up pitch torque in cruising flight, to prevent the helicopter from nosing down.  The answer appears to be generally "no".  Of course, if such a pitch torque were necessary, it would be simple enough to position the cyclic as needed to create such a torque.
Now, if you were to ask what happens in the first instant after we use the cyclic to tilt the rotor disk forward in a hover, when the forward airspeed vector and therefore the rearward Drag vector acting on the fuselage are not established yet-- as the top figure with the tilted rotor disk appears to illustrate-- that would be an entirely different question.
Note that none of this really addresses whether the system is stable or not.
Many assumptions have been made here, but maybe this answer will give you a starting point for looking at your problem.

Thanks for answering. May be this image can help. https://imgur.com/5f2EAsr
I am assuming the CG is ahead (front) of the Lift vector. (Is this assumption correct?)
Based on this assumption, the lift force generates a downward pitching moment Lx, which can increase further if the cyclic is increased, leading to higher value of x', and hence higher moment  Lx'.
How will the free body diagram for balancing the moments about CG, be - during forward flight.

"Not ... true while system is accelerating", but true when it is not! Good step forward here, old school "Schriftsteller der Wissenschaft" take note!

@RajArjit -- answer completely revised.  There's a lot more to the problem than I realized.  Good question.  And again, I'm just thinking it through, don't know much more about helicopters than I've included here.

See https://aviation.stackexchange.com/a/77811/34686 for a better answer

In many ways helicopters are air planes in disguise.
First, you draw the rotor with a slight dihedral.  Now draw the lift vector for each rotor and you find:  it will actually try to pitch the aircraft back upright (after forward acceleration goes to 0 (constant speed))!  Even if the rotor were perfectly straight, its lifting force will not create a pitching torque unless the center of gravity is off-set.  (draw dotted lines for the rest of the helicopter too).
Center of drag (as viewed from the front) will also be a factor once the helicopter is moving.
The downwash of the rotor on the tail also plays a role.
However, pitching forward, without increased power, will cause the heli to sink because the vertical lift is less. The upward drag aft of center of gravity will cause it to pitch down just like an airplane.
If you pitch forward and add enough power to climb, you may find the nose pitching up!
So you add just enough for level flight.
The concept of "pitching forward" and adding "power" from hover is identical to V min sink rate compared to V "best glide" in airplanes.
Perhaps a bit like this:

Thanks for answering. Maybe this image can help. https://imgur.com/5f2EAsr
I am assuming the CG is ahead (front) of the Lift vector. (Is this assumption correct?)
Based on this assumption, the lift force generates a downward pitching moment Lx, which can increase further if the cyclic is increased, leading to higher value of x', and hence higher moment  Lx'.
How will the free body diagram for balancing the moments about CG, be - during forward flight.

A smart design would be counter balance with rotor wash downforce on tail.  So make little fins there until it is right.  Note "throttle" will be more for moving flight than hover in all cases.

May you please tell how is the tail's rotor wash controlled? As far as I know, only collective input can be given to tail rotor and that too in lateral direction.

The down wash of the main rotor on the tail is what I was thinking.  It will vary with throttle input.  Other possibility would be a 3rd "pitch rotor".

@Raj Arjit after giving more thought, there are probably more things trying to pitch it backwards when power is added, so some forward pitch torque may be a solution, not a problem.

— I thought my question was very basic, there must be some simple solution to it.

Probably build into the design, rather than control. Your diagrams are good.  Note when the rotor is tilted forwards, it's "wash" will strike more of the tail.

Okay. If possible please upvote my question, so maybe more experts can see and answer it.


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Helicopter retreating blade stall: Increasing the fwd speed decreases the tip speed on retreating side and angle of attack. So why limit on V_n.e?
On Retreating side: Speed of wind over blade tip  = blade rotation speed - forward speed.
So, with an increase in forward speed, the speed of the wind over tip is getting reduced. In airflow diagram, this will decrease the angle of attack. So, why is there a limitation on forward speed in form of V_ne?
Let's consider a case where rotor of radius 10m rotating at 300 rpm anti-clockwise and chopper is moving forward at 30m/s. So, now the retreating side has got a larger angle of attack of 15 degrees (critical angle is 17 deg) due to blade flapping down. Blade tip speed being = RPM x radius - forward speed = 314-30 = 284m/s.
"Now" if the helicopter fwd speed increases to 50m/s, then the blade tip speed will decrease to 264m/s. Consequently, the angle of attack should reduce.

Is it because - to go at high forward speed, I have to increase pitch angle on the retreating side?

check this link, it explains the phenomenon in detail. Unfortunately, Helicopter aerodynamics is not as rigid as your sketch shows, the blades are flapping wildly :)
https://www.skybrary.aero/index.php/Retreating_Blade_Stall

@GürkanÇetin: It doesn't help. I got this question after reading from that page itself. In the image it says, blade tip speed = speed of rotation - forward speed. So, higher the forward speed, lower will be blade tip speed. Hence the question.

In theory the limitation can also be related to mach# of the advancing blade tip, but only on very fast helicopters. This answer covers it well https://aviation.stackexchange.com/a/16958/30504.

The angle of attack is not higher because of any inherent property of the rotor, it is higher because of pilot input.

For the same reason aircraft have $V_{S}$ — you don't want to get into stalled condition, because while recovery is possible, it is difficult and far from certain.
Due to the gyroscopic effect, the rotor blades reach the lowest point 90° behind the point of minimum lift. As the helicopter accelerates, the lift would decrease on the retreating side, which would push the aft side of the rotor down, pitching the helicopter up, and reducing the speed again (that is, unlike hover the helicopter is stable in forward flight).
Except the pilot wants to accelerate, so they keep pushing the cyclic forward, which increases the angle of attack on the retreating side (90° ahead of the desired tilt to compensate for the gyroscopic effect), compensating the loss of lift due to the lower air stream velocity.
So the angle of attack is higher on the retreating side because of pilot input, not inherent property of the rotor.
Now when the helicopter reaches the point of stall, the tendency to pitch up will increase, and it won't be possible to compensate it with more forward cyclic, since the retreating side is not able to generate more lift. In this sense, the condition is actually self-correcting as the helicopter will start climbing and losing speed. However

the accompanying vibrations from the repeated stalling and unstalling of the blades as they rotate will stress them significantly and might cause structural damage and
the violent pitch up accompanied with some roll to the retreating side (which it is depends on type) might lead to the pilot losing spatial orientation and consequently control over the usually low flying vehicle.

So you still want to avoid getting into the retreating blade stall condition in the first place.

How does an increase in helicopter speed increases the angle of attack at the tip on retreating side? Blade tip speed = speed of rotation - forward speed. So, with increase in fwd speed, blade tip speed reduces. This should be beneficial. Where am I wrong?

@RajArjit, the angle of attack is controlled so that the blade produces the same amount of lift on either side, otherwise the aircraft would tilt. Since the retreating blade is moving slower, its angle of attack must be higher. No, it's incidence angle (angle relative to the mast) is not the same. That's what the cyclic control is for.

Let's consider a case where rotor of radius 10m rotating at 300 rpm anti-clockwise and chopper is moving forward at 30m/s. So, now the retreating side has got a larger angle of attack of 15 degrees (critical angle is 17 deg) due to blade flapping down. Blade tip speed being = RPM x radius - forward speed = 314-30 = 284m/s. "Now" if the helicopter fwd speed increases to 50m/s, then the blade tip speed will decrease to 264m/s. Consequently, the angle of attack should reduce.

@RajArjit, but the blades won't keep moving along the same path with the same incidence – between increased flapping and increased cyclic they will move so they still produce the same lift, and to do it at their lower speed, their angle of attack will increase. Because they must keep producing the same lift to keep the helicopter flying straight.

From the hover as the airspeed increases the retreating blade is effectively slowing down due to the forward airflow. Despite this, the blade still maintains the same amount of lift as the advancing side, it can only do this by progressively increasing the angle of attack.

@RobWilkinson, actually, the retreating blade would not maintain the same amount of lift if it was not commanded to. But it is.

I’m unclear about your comment  ‘unless if it was commanded to’ ?

@RobWilkinson, the retreating blade does not maintain the same amount of lift as the advancing one due to any inherent property of the rotor. It only maintains it because of forward tilt of the swash plate that reflects forward pressure on the cyclic.

As the helicopters speed increases the angle of attack on the retreating blade will continue to increase. Due to the rotational velocity increasing along the length of the blade, the angle of attack will be greatest at the end. It is this area as the speed increases combined with the blade flapping down which will stall. ('Berp' blades (looks like a paddle on the ends) are designed to retain the boundary layer by creating  vortices at the ends and can achieve AOA upto 22-degrees so are designed specifically for high speed flight). When looking overall at high speed flight and Vne, other limitations need to be considered such as airflow reversal which will be occurring at the root on the retreating side (and growing outwards as speed increases), compressibility of the advancing blade and jack stall with the increasing loads which may affect smaller helicopters. Together these will effect the helicopters published Vne. Additionally, if you flew any helicopter on a calm day, straight and level continually increasing speed there would be a point the above aerodynamic effects would occur, assuming you were not first limited by engine/gearbox limitations or lack of forward cyclic position. Whilst this speed could be regarded as Vne, the precise figure needs to consider density altitude (Vne reduces with height), high G manoeuvres, rough/excessive control inputs and turbulence, all of which will lower the maximum speed and will be taken into account for the aircrafts published Vne.

Hi Raj, To further answer your question below.
If the Blade tip = speed of rotation - forward speed hopefully you would agree the reduction in speed of the retreating blade would cause a loss of lift. In which case the helicopter would roll in that direction (notwithstanding phase lag etc). So before you consider what's happening with high speed flight you should understand how lift is maintained equally across the rotor disc in normal flight. If you consider the lift formulae, you can create more lift by either making the aerofoil go quicker (the advancing side) or increasing the angle of attack (retreating side). This is precisely whats happen with the rotor disc. Consider a rotor blade in forward flight starting in the 6 O'Clock position and rotating Clockwise. As it move to the 9 O'Clock position it gains more lift by the virtue of increasing speed. In doing so it flaps up. As it flaps up the induced flow increases which reduces the angle of attack. (The blade reaches it's max rate of flapping up in the 9'oclock position and it's highest point at 12 O'clock position). As the blade travels towards the 3 O'clock position, it starts to lose the airflow over the blade so begins to flap down. As it flaps down the induced airflow reduces and the angle of attack increases, maintaining the same amount of lift this time with a large angle of attack and low air speed (again, the maximum rate of flap down is in the 3 O'clock position and the blades lowest point will be back in the 6 o'clock position). This is how lift is maintain constant across the disc at all times (except when manoeuvring or problems with high speed flight) and why the angle of attack increases on the retreating side. It's called 'Flapping to Equality'

Your first sentence is - "As the helicopters speed increases the angle of attack on the retreating blade will continue to increase." - How? How does an increase in helicopter speed increases the angle of attack at the tip on retreating side? Blade tip speed = speed of rotation - forward speed. So, with increase in fwd speed, blade tip speed reduces. This should be beneficial. Where am I wrong?

All else equal, you are correct that the angle of attack on the retreating blade tip will actually decrease, not increase.  As you calculated, the horizontal component of the flow shrinks, causing the inflow angle to grow (and effectively shrink the angle of attack).
However, the "all else equal" isn't realistic.  Unless there's angular acceleration of the rotor/aircraft, the lift is balanced around the rotor.  The lift on the retreating side must approximate the lift on the advancing side.  This is accomplished with forward cyclic and blade flapping.  Since the dynamic pressure on the retreating side is smaller, as you pointed out, the cyclic/flapping made the angle of attack much larger (to balance the lift).  It's this net result, after accounting for cyclic/flapping, where you can see the retreating stall must eventually occur.


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Why is the JAC VOR an Initial Approach Fix for the KJAC VORDME Rwy 19 Approach?
See the attached KJAC VOR/DME Rwy 19 approach.
QUESTION: Why is the JAC VOR an IAF for this approach?
There isn't a procedure turn to use this VOR as a functional IAF,
and the twin peaks (13,770' & 12,695' plus 7,139') should be enough to disuade you from trying while IMC.
The FAA Instrument flying handbook defines an IAF as:
Initial approach fix (IAF). The fix depicted on IAP charts
where the instrument approach procedure (IAP) begins unless
otherwise authorized by ATC.
The chart doesn't indicate radar contact required. I don't see any other route from the VOR JAC IAF to establish one's self on the final approach.
Hence the question on why the reason for labeling the JAC VOR as an IAF for this approach?

I don't have an answer but JAC isn't marked as an IAF on the FAA plate. Perhaps a charting error by Jeppesen?

@Pondlife beat me to it but that is my conclusion as well.

@Greg I tried to transform the title in a question (we're on a Q&A website) but I'm not quite sure it completely reflects what you're asking. feel free to edit it again.

Thanks I edited the title. Why is the JAC VOR and Initial Approach Fix for the KJAC VOR/DME Rwy 19 approach?

It's not an IAF according to the FAA approach plate:

Besides not being identified as an IAF, JAC could only be an IAF if there was a charted course reversal.  As the FAA approach plate specifically says "Procedure Turn NA" that possibility is ruled out.


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Why is EASA CS 25 non-binding?
EASA states that Certification Specifications (e.g. CS-25) is non-binding on their website. See the regulations structure PDF.

Each Part to each implementing regulation has its own Acceptable Means of Compliance and Guidance Material (AMC/GM). These AMC and GM are amended along with the amendments of the regulations. These AMC/GM are so-called ‘soft law’ (non-binding rules), and put down in form of EASA Decisions. A comprehensive explanation on AMC in form of questions and answers can be found on the FAQ section of the EASA website.
Furthermore, Certification Specifications are also related to the implementing regulations, respectively their parts. Like AMC/GM they are put down as Decisions and are non-binding.

The FAA's 14 CFR 25 is certainly what I would interpret as binding or required. As a manufacturer you are required to show compliance to applicable parts of 14 CFR 25.
What does EASA mean then? Or what are they trying to communicate about Certification Specifications such as CS25? Or what is different about their organization that makes CS-25 “non-binding”?

why did you remove the quoted text? In my opinion, it was much better before. Now people have to follow the link, open the PDF, and find the text you refer to. It's much simpler to include the relevant quote here (in addition to the link), especially for users on mobile devices.

@Greg the SE model is based on co-operation. This includes editing posts from other users to improve them and bring them up to the standards of the community. You are free to ignore the suggestions, of course, but be aware that the other users are trying to help you.

The reason is that EASA cannot provide legally binding interpretations of EU Regulations, and the Certification Specifications are an interpretation of the EU Regulations.
Within the European Union (EU), legally binding interpretations of the EU regulations are exclusively provided by the national and EU courts and the European Commission.  The EU Member States are responsible for interpreting and implementing EU law in their national legal system.
The European Commission (EC) has created the European Aviation Safety Agency by decision EC 218/2008, recently repealed and succeeded by EU 2018/1139. The EC tasked EASA with creating certification specification and other material:

EU 2018/1139, Article 76
...

The Agency shall, in accordance with Article 115 and with the applicable delegated and implementing acts adopted on the basis of
  this Regulation, issue certification specifications and other detailed
  specifications, acceptable means of compliance and guidance material
  for the application of this Regulation and of the delegated and
  implementing acts adopted on the basis thereof.

And thus EASA is tasked with creating certification specifications that allow application of the high level EU aviation safety regulations, which requires of course the interpretation of those regulations.
At the same time, they don't have the power to give a legally binding interpretation, because that is reserved for the national and EU courts and the EC.
Consequently the Certification Specifications published by EASA that give the required detail to comply with the regulations, are not binding. They are referred to by EASA as "soft law", whereas the Regulations and Implementing Regulations on which they are based and which are published by the EC are referred to as "hard law"
As an aircraft manufacturer, you may argue that there are alternative ways of complying with the EU aviation safety regulations (hard law), whilst deviating from the Certification Specifications (soft law). If you make your case well, you will still get a type certificate.
This is not any different in the US, where aircraft can be certified with deviations from FAR 25. You don't necessary need to show compliance with all of FAR 25, if you can convince the FAA that the deviation from FAR 25 is reasonable and safe, a type certificate will be granted.
For example, see this table of granted exemptions from FAR 25 for the Boeing 737-8 and 737-9:

source: 737 type certificate(PDF)
Relevant EASA FAQ's:

What are the areas of responsibility for the Agency?
What is the definition of an IR, AMC and CS and GM and what differences can be proposed?

I understand most of your impressive response. Where I struggle to connect, is with the phrase “they” (the agency aka EASA) “don't have the power to give a legally binding interpretation”. While this make sense and I have no doubt it is true, if a manufacturer requests an Exemption, ELOS, etc. in regards to a CS, would not EASA then have to give a legally binding interpretation of 2018/1139? EASA would need to assess and interpret the basic regulation 2018/1139, to ensure the request (e.g. ELOS) met the intent of 2018/1139?

Per 2018/1139 Article 76 (1.) & (3) does this mean EASA produces the proposals (e.g. Certification Specification, AMC) and then must have them approved by the EU Commission? The language of “opinions” gave me that impression.

Hi Greg, good follow-up questions, I am afraid I don't have an answer for you off-hand. I was trained as an aerospace engineer, not as a lawyer, so I am out of depth on this level op detail. I find the subject interesting, and I'll try and research a bit more, but don't hold your breath. Maybe somebody else will chime in with a legally binding answer :-)


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Is it possible to identify plane engines by sound alone?
Can airplane engines be differentiated and identified by what noises they make? If so, what does each engine sound like? How would you be able to tell between a low-bypass and high-bypass turbofan? How could you tell between turboprops and aviation piston engines?

Please see if the answers here give you a good answer to your question.

@RalphJ I was wondering if you could tell what type of engine is being used, like turbofans or turbojets

Yes, but it's not something you can just easily explain, you have to listen yourself to discern differences.

One of the more subtle running gags in the movie Airplane! was the piston engine airliner background sound even though they were in a jet.

@JohnK, it isn't always an intentional gag; in one of the latest Jurassic Park movies they dubbed a piston engine sound into a 208 Caravan.  Because, you know, that's what prop planes sound like, right?!

Anecdotally, I grew up under the NAS Moffett Field flightline and heard P-3 Orion aircraft flying overhead daily. A couple of years ago, I heard a plane and thought "that sounds exactly like an Orion". I was wrong; it was a C-130. Both types fly on 4 Allison T-56 turboprop engines.

Regarding only piston engines: with practice you can identify 4-cylinder engines, 6-cylinder engines, 2-blade props, 3-blade props, horizontally-opposed engines, and radial engines.
There are certain classic piston engines that have unique characteristics, like those used in the twin bonanza, which are readily recognizable because they were geared (turning faster) and had "augmentor" exhausts (distinctive exhaust note).

True.  You can always recognise a Merlin engine.

To a certain extent, yes.
As per your question, low and high bypass ratio engines are quitw easy to learn to tell apart. From close(ish) low bypass engines are stupid loud, and the sound spectrum is quit even, offering deafening experience in all frequencies. High bypass engines tend to be clearly less noisy, the bypass fan contributing a "swooshing" note to the sound.
Another way to describe the difference from close range would be to call low bypass engines' sound "raw" and that of high bypass engines softer. Also some passenger plane high bypass ratio engines have a noticeable "growl" at high power setting, sorry to say I can't tell which make/model it is off the top of my head.
Further away low bypass engines will be audible as a low rumble, and high bypass ones as a more even noise.
As for the piston vs. turboprop part: this really is a no brainer once you learn to distinguish the propeller noise from the engine noise, since a lot of the noise of propeller driven planes actually comes from the propeller itself. The exhaust "purr" of a piston engine is easy to tell apart from the high pitch whine of a turbine engine, which also has a distinct exhaust "swoosh" similar to that of a high bypass jet engine.
Combined with the "aerodynamic noise" made by the airframe  creates more or less unique sound footprint which in turn can be used to narrow down the specific engine, on a further note on that: I live near an active military base. I can tell by sound alone which of the few "domestic" types is flying by, even at miles away. During joint excercises I can also distinguish visiting types from the usual ones. Determining the engine would then be a matter of looking up what engine is run in which airframe.
I'm confident an algorithm would be able to quite accurately recognice most of current engine/plane combinations if it had a large enough database to reference.

I know that there is technology that analyzes the sound signature of submarines and traces their locations and what country they're made by, as designs differ between countries. I would assume that a similar model could be applied to aircraft, where an ML model could be trained to make the comparison between engine type and sound profile, and then pair that with a list of possible aircraft.


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What is a normal EGT range of a jet engine?
Out of curiosity at what temperatures are the exhaust gasses are expelled from jet engines? A normal reciprocating engine from what I recall should be in the 700 - 1100 degrees Celsius range. Does this apply to turbofans/turboprops/turbojet engines also since the fuel properties should be similar? Or are the temperatures much lower as the engine is being used mostly at high altitudes?

Turbofan without afterburner
In non-afterburning engines the exit temperature inside the nozzle is around 600°C at full continuous thrust. If the ambient temperature is low, less heating is needed for the same thrust, and exit temperatures are lower. The maximum temperature for a given engine is, however, independent of altitude and given by the materials inside the engine. In flight the continuous maximum can be higher than on the ground, when the cooling by the external flow is less effective.
Temperature profile at a distance
This report gives results of ground measurements on the Pratt & Whitney JT8D of the Douglas DC-9 and shows how quickly the temperature drops behind the aircraft due to mixing and radiation.

Jet temperature behind a DC-9 at take-off power. Picture source.

Jet temperature behind a DC-9 at idle power. Picture source.
With afterburner
With full afterburner the engine uses approximately five times as much fuel as when running dry, and it shows in the exhaust gas temperature. This report details measurements of nozzle pressures and temperatures on one of the General Electric F-404 engines used in the X-29 program. The plot below is taken from the report and shows exhaust-jet temperature summaries in the horizontal centerline for various power settings (PLA = power level angle; 120° is full afterburner and 87° is military thrust).

Nozzle temperature survey of the GE F-404 afterburning engine. Source.
The test conditions were 30.000 ft altitude and Mach 0.3, simulated in an altitude chamber. The temperatures were measured with a rake just a few inches aft of the engine nozzle. Note that the temperatures are given in Rankine; the maximum of 3800°R is 1838°C. The wake of the engine's center body causes lower temperatures in the center of the jet at XSRL = 0. The nozzle edge is at 12.7 inches from the center; due to symmetry only one half of the jet temperature profile is shown.

@JanHudec: Sorry, but I removed the part on the GE-90 as it did not really fit here.

The exhaust gas temperature of a jet engine depends on a number of parameters like,

The operating conditions
Whether afterburner is used or not
The condition of the engine
Type of the engine (whether low or high bypass turbofan etc)

Without after burner, the exhaust gas temperature is around 600-650 $^{\circ}$ C, which goes upto 1500 $^{\circ}$C with after burner. The figure below shows the data for General Electric J79 low bypass turbofan engine.

Source: www.aircraftenginedesign.com
In case of high bypass turbofan engines, the exhaust gas temperature is slightly lower, usually around 500-600 $^{\circ}$ C. For example, the figure shows the temperature variation in PW 4000 engine.

Source: web.mit.edu
The temperature of the engine is determined by the materials used, especially the turbine temperatures (and method of cooling), and not much on outside conditions. As such, the turbine gas temperature is the highest temperature in jet engines and the limiting factor.
The Exhaust gas temperature is a parameter to measure engine health. A high EGT for a given thrust (by a engine) is a sign that the engine required more fuel for the same thrust, due to wear out of rotating components, etc, and the engine may require inspection.